Does a car speedometer measure speed, velocity, or boicvgu)z m0+nv8, 1pvz th?

Can an object have a varyvx21tjm kt /v+gfg,(it 5cs e+ing speed if its velocity is constant? If yes, give examt+v kgf tjt(vc+51g,/x2 iesmples.

When an object moves with constant velocity, does its a cpf/46ru bj;overage velocity during any time i/ f;6brpj ou4cnterval differ from its instantaneous velocity at any instant?

In drag racing, is it possible for the car with the greatest speed(,a.0ag6vmj(twtx w b crossing the finish line to lose the race? Explaig (bxt(wvj6wm. ata,0 n.

If one object has a greatea1/ao,pcpm3 m3p9 p/rblh1pj r speed than a second object, does the first necessarily have a greater acceleration? Explain, using exampler9om pl bp,j1pm3apha p//c 31s.

Compare the acceleration of a motorcycle that acgzj rr/8iwaio*ygi0ks/ **m 5 celerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 10km/h in the sam5kmgirs* *80a r/io*/yziwj ge time.

Can an object have a northward velocity and a southward acceleration? Epysdb 4ezw 6y9y9.qu)5j*gs g xplain.

Can the velocity of an object be negative when itam,d.mtr nfafn2 . 16us acceleration is positive? What abof,1..nfdr n6maatu2m ut vice versa?

Give an example where both the velocip l6m62 wl3(p u1 nbltz+-vykhty and acceleration are negative.

Two cars emerge side by side from a tunnel. Car A is traveling with a r*d rtob/t+(v b9r rfp*ky4i5g b.v5w speed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the otherry+br9 ( . 5gbrd*5rfvi4ovptk/b*wt as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleratio0 ez k4;mvv4yuvn)y z)n decreases? If so, give an ex0v4vvnze4u m)z)k;y yample. If not, explain.

A baseball player hits a foul ball straight up into the air. It leaux(yy8 e0w ;vwkdw +()p;zvobves the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be travvz;+uwd wek; y8yp ob(( w0x)veling when the catcher catches it?

As a freely falling object s:zt-an7 7s e*5si 4ovk avj/wepeeds up, what is happening to its acceleration due to gravity — does it increase, decrease, or st:o vs e7vekjn-t4/ai*7s 5awzay the same?

How would you estimate the maximum height you could throw a wj 92leq/zkh: 2cea4jball vertically upward? How would you estimat9w 2lchz4ke2 e jq/:jae the maximum speed you could give it?

You travel from point A9/ kerbw-ukp: to point B in a car moving at a constant speed of Then you travel the same distance from point B to another point C, moving at a constant speed of 90km/h . Is your average speed for the entire trip from A to C 8:/9rbkkwu ep -0km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-locx ml1uk(- (7jw v6jmung vertical string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a t6(7cwju-u 1 jlmvk x(min plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is not at constaxy-p). 8e;vgp jmfll/lz(u7qnt acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor makinl(8;yp ll.p uxg )fvjz q7-em/g stops along the way, a dish resting on a table?

An object that is thrown verticallyvgj1orf3 pc1h3 y:annp057cl upward will return to its original position with the same speed as it had initially if air resistance is negligible. If air resistan nfhjy71 rlpnp350oa 1 c3v:gcce is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance is always in a direction opposite to the motion.]

Can an object have ze lz8j*ns pnlu7n dy,54ro velocity and nonzero acceleration at the same time? Give examndzys8*n,pn l jlu 745ples.

Can an object have zero acvc kdrr7pu 8pco2. f0s0n9ha5celeration and nonzero velocity at the same time? Give kp ah2pdc 0n uc7v0r fs5ro.89examples.

Describe in words the motion ploq0vl *tl+ l3x:t x1slctted in Fig. 2–28 in terms of v, a, etc. [Hint: First try to duplicate the motion plotted 0*xl tx:t+3l sq1 vllcby walking or moving your hand.]

Describe in words the motion of the object grap zugs57qam)1lhed in Fig. 2–29.

  What must be your car’s average spe/(c:1t04 koq sedwxucya :+d xed in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How lohs3k4 (/:o+3 tgvcr +vxuj nksng does it take to fly 15 km?    h

  If you are driving along a straight road and you)n8gkx4z a.48uznee m:lrwvef j j 0:re1cq)1 look to the side for 2.0 s, how far do you travel duzej l1 gxzam8rjf)we cn418) kq4.e:n0e :vruring this inattentive period?    m

  Convert 35 mi/h to zf6n816(u:e1kyo es xl p- fxh)wnv,i
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from .-q7 quhyx0p7nce8pp/pmo o3;vion) $x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

  A particle at $t_1$ = -2.0 s is at $x_1$ = 3.4 cm and at $t_2$ = -4.5 s is at $x_2$ = 8.5 cm What is its average velocity? Can you calculate its average speed from these data?    cm/s

  You are driving home from school steadily h k2f . l/sy,hpmdxev)txmdjt:i6;07at 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h Youyts:.pj6ht;m2,/vmddxx) 0 if kl7 eh arrive home after driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-t z/mliv wk 676cd(xz4vhumb, every five seconds between a lightning flash and the followinm(czd4xv7l 6 vikw 6z/g thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile track in a total timbp/py3ub4c/3gwh qj+ foij/ . e of 12.5 min. b3/4+ip./o/j c q3y wbgphjufCalculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trai1 ;no/,cr*n6u5ob jk ksbvyh 6ner in a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops halfway back in 4.jbn;k6b*c yk1s 6o5hou/rnv,8 s. Calculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach each other on parallel tracks. Each has a a+1 u9ge enu8lspeed of 95 km/h with respect to the ground. If they are initially 8.5 km ap9en8+u1 ulag eart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behind a truck traveling How long will idq-.ci n4:pqlt take - p.lqcn:i qd4the car to reach the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encounz /djakzdec, v:a* 9m/ters a tailwind that boosts its speed to 990 km/h for the next 2800 *a d /jm: cza,dkve/z9km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average speed and average velocity of a complete round-tr p /zpk/eyucm(5ffr7/ip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250mf/5k z yp e(/urpf/c7 km is covered at 55 km/h.    km/h

  A bowling ball traveling with constant speed hits th6+*iwpe mcp -q4j ke,gi8gd7e:8 ztyb e pins at the end of a bowling lane 16.5 m long. The bowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from b gdp8 ck6wg7j e8:ymiez*,-4 pti+eqhis hands. What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 sltwj ;r0fgz 8*v 1/z3:nmv bkg. What is its average acceleration inljk3v ;vmg:*z rz f/80gbw1t n $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her accelerati5dn6j)srib,f fcll793rn))hr1 e v rf on n5j6r7)vc 3rsf f)nrdilrf,e)l hb 19
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile is capable of an acce vgna*c,uyf7 p 69 l4yd /yf0nzpjc7o:leration of abou4covfp6p n77, f /u 0jdy:l*ynyagc9zt $1.6 m/s^2$ At this rate, how long does it take to accelerate from 80 km/h to 110 km/h ? $\approx$    s (Round to the nearest integer)

  A sports car moving at consta b(u5b n3m7:avmt/fg gnt speed travels 110 m in 5.0 s. If it then brakes and comes tv u( /gb3nf a5mm7gt:bo a stop in 4.0 s, what is its acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which starjh1/ k z5a am8q:mn-p /-nuvvdts from rest at t = 0 and moves in a straight line, is given as a function of time in the following Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display khz/nvupaq1-d8mj n 5:av-m / each in a Table and on a graph.

  A car accelerates from 13 m/s to qiyp5m uh(3mam.y3lbfw* p:8o .n5z y25 m/s in 6.0 s. What was its acceleration? How far did it travel in this time? Assume constant acceleray8 (mf*lq5b 3zwpmpuam3 .oyh i5:n.ytion.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 85 m. Wukfq6n2sd +l :hat was its accelern us+fqd:k 6l2ation, assumed constant?    $m/s^2$

  A light plane must reach a speed of 33 m/s for takeoff. How lon : jiq8l+cr4czg a runway is needed if the (constant) c:8j4ql+i czr acceleration is $3.0 m/s^2$ ?    m

  A world-class sprinter can n 1/bbwca :pw.burst out of the blocks to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprinter, anpa1nw c:b/. wbd how long does it take her to reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down unik(df.2wu9 1 yrueuz9j* )liow formly from a speed of 12.0 m/s to rest in 6.00 s. How far did it travel2udw)19izlk orf. y (j9uu*ew in that time?    m

  In coming to a stop, a car leaves skid marks 92 m long on the highway. Ass.ig7crc, q k+cuming a deceleration of c+ .gk cc,irq7$7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The front end og 9q. qwew2/mpf the car compresses and the driver comes to rest after traveling 0.80 m. What was the average awmwq qp29g /e.cceleration of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car wkhehtc80 ihafs sn3125 imc (2ith an initial speed of 95 km/h and human reaction time of 1.0 s, for an acceleration h(hefnmct10c i22s5iak8hs 3
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation for the st cwk:px,-m j7ropping distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 m/s on t-vhm8afs.. 3klg;6nyb4ao .aa (izz qhe highway. The car’s driver looks for an oppz bn i-4a6 gfaksozvl8.;.3hmq (ya.aortunity to pass, guessing that his car can accelerate at 1.0 $m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000-m run in less than 30.0 min. After e5ccjy kuleoly;9og- 8wp0cluym5 8)5 xactly 27.0 min, there are still 1100 m to go. The runner mus 5u58;pcy-ycc )08ego lml loj5u 9ykwt then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approaches an interse +l ch4f o zr5/ph+s03ccv* cxzwu-mo/ction just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersrh+f0uhxoc 5 p/-ozwv3*lcc/ +sm4zcection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hits the ground below afterkmgs r d rhw4pwz2e//b6fo77xh, w ..r 3.25 s. How high ihz2/wbr,roh.7k mpw wr7f e dxs4g6. /s the cliff?    m

  If a car rolls gently .l 0qmi*qr8,pc. nkmz($v_0\,=\,0$) off a vertical cliff, how long does it take it to reach 85 km/h ?    s

  Estimate
(a) how long it took King Kong to fall straight down from the top of the Empire State Building (380 m high), $\approx$ =    s (retain one decimal places)
(b) his velocity just before “landing”?    m/s

  A baseball is hit nearly straight up inu((xj yjswqzo r 3-*k0to the air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a ball 3.0 s after tn:bv7l (k31f zslhy- shrowing it vertically upward. With what speed did he throw it, and what height -v:1s3slhblf zy( 7k ndid it reach?    m/s (Round to the nearest integer)    m

An object starts from rest and falls u0kwr h,ez;82vg 7yefdnder the influence of gravity. Draw graphs of (a)7 vwe;g ky, 02zd8erhf its speed and (b) the distance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed pv/8q )chge6;tr+b ayof 5.20 m/s. At a height of 125 m above the Earth, a package is dropped from a window. How much vhgtr+ abq; /p8e)cy6time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the dista,w +kid)s /c 7pvlki1dnce traveled during each successive second increases in the ratio of successive ,kd+lswi1/dc vp7k) iodd integers (1, 3, 5, etc.). This was first shown by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglec, h(qd 9uyocv+ted, show (algebraically) that a ball thrown vertical +9o qdhyc(uv,ly upward with a speed $v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upwpqbpfai f2:.6 +w3:a is pg9lnard with a speed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between eac3i e3pfyl fx,)h photoflash of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclea f3e3pxlf,i )yr ones at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tall (Fig. 2–32). Fro bn-)squ k1b*em what height above the top of the window did the st*)1ubqs-k ne bone fall?    m

  A rock is dropped from a sea cliff, and the sound3votjoeq z ); +kxa*2m of it striking the ocean is heard 3.2 s later. If the speed of so vjt xz3m);o2ekaq*+ound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust your garden hose nozzle for a hard stream of watq*o3;3n f;j; yj mwqqler. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hq3monw jqyq ; ;*j3;flear the water striking the ground next to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upp ucm lkdn6yo04 03vbj-fa:y1 o/ekx6ward with a speed of 12.0 m/s from the edge of a cliff 70.0 jf3ykd0o l bxmku :a-/nye4v 6p61oc0m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 m above the street ;bdd-(l88iip ptcc,nwith a vertical speed o8 ddp8ni, ;b(t lcipc-f 13 m/s If the ball was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocityd lor 8zp9g2k3cd z0*t of a train as a function of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what periods, if any, was the acceleration constant?8cz2 *o3kd0r d9zgltp (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a funn *usir( m dx-+b3yhve)h( 9bz1y8qejction of time is plotted in Fig. 2–28. d( u*)9y8 vx(hj-ze3 m ebrinb hsq1y+What is its instantaneous velocity
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

  In Fig. 2–28,
(a) during what time periods, if any, is the velocity constant? t =    s to t $\approx$    s
(b) At what time is the velocity greatest? t =    s
(c) At what time, if any, is the velocity zero? t =    s
(d) Does the object move in one direction or in both directions during the time shown?

  A certain type of automobile cp )+y .za92eaae/ig;p r/ftdwan accelerate approximately as shown in the velocity–time graph of Fig. 2–35. (The).aaeet pr gdyif 2+;9z w//pa short flat spots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the car in the previous Pro4z.*uh58wxr 7c )gvn5gypioym )b ,di blem (Fig. 2–35) when it i)mv48u ywc).zo g5h x bryidp 7,*gi5ns in
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the object c,ny2wbaf4hn (/bo;z traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the qvo1-zgxoj0w, d vi-kj0.7svobject whose displacement as a function of time is given by Fig. 2–28kj07o0o iwv zxd qvjgsv,-.-1 .

Figure 2–36 is a position versus time gwus9)8wq-iuh u : rn9craph for the motion of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direr) qi9un:u- wwushc 98ction? (b) Is the object speeding up or slowing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourth-story window 15.0 m above a firefighter v3d wkrc;x*6s’s safety net. The survivor stretches vw;6 rxs3cd*k the net 1.0 m before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about o7j8u xoun5m0 one-sixth what it is on Earth.7u5u jxn0oo m8 If an object is thrown vertically upward on the Moon, how many times higher will it go than it would on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-shoulder seat belt has a g izu tw62olmc1bzf.) 4ood chance of surviving a car collision if the deceleration does nmo .i1tu4wcz lfb2z6)ot exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standing on a bridge, 12 m above the road below, and his purx:n7-tbypx2b9 tw (stsuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing that the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m at7s: p(9b nttbyxw2-x bove the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufacturer tested its cars for front-end dip,2:e zbjc2rw8l; et -k5:l tx +yticollisions by hauling them up on a crane and dropping thl iwc:z d,:e-kt;8tijpel ty+x22r5 bem from a certain height.
(a) Show that the speed just before a car hits the ground, after falling from rest a vertical distance H, is given by $\sqrt{2gH}$ . What height corresponds to a collision at
(b) 60 km/h ? $\approx$    m (Round to the nearest integer)
(c) 100 km/h ? $\approx$    m (Round to the nearest integer)

  Every year the Earth ttwce/,(i9). bvlqnxh ravels about $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins uniform ;dr8gv(p c,q d71rg9(k fsxnu acceleration from rest. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where k(ds7f pu1q,dx8 (; rrggcnv9 the front of the train started. What will be the speed of the last car as it passes the worker? (See Fig. 2–38.)    m/s

  A person jumps off a diving b(+b ij1o btsmu2/oea1 oard 4.0 m above the water’s surface into a deep pool. The person’s downward motion stoptoi+s ob(mbe /j11ua2s 2.0 m below the surface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessary to balance the j+hmrmdut1 5ea66)bj average speed of a train against the distance between stops. The more stops e1bj)mut 6dhr5+6 mjathere are, the slower the train’s average speed. To get an idea of this problem, calculate the time it takes a train to make a 9.0-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends);    min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s.    min

  Pelicans tuck their d/3pl0dhl6zo 67rsdw -*ta x pwings and free fall straight down when diving for fish. Suppoo3p0*z /xph-a7 sdddl6w r6ltse a pelican starts its dive from a height of 16.0 m and cannot change its path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer oy- gwm wbo,fuz;1lb(fm:r8 -strikes a ball is planned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, smz-lfo,y b:;gf wb18uw( -ormee Fig. 2–39) is more difficult than from a downhill lie. To see why, assume that on a particular green the ball decelerates constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freight train travelir2/t2uby6b60.y9 ar 6rp egyaphb4 t xng at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive starts from rest and accelerates a xety6r9/b a ptby 2a6.pb rgh6y4r0u2t $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high building. A second ston9 z6bj3 6 lcfcf g1fc3yg yq19szyra:0e is dropped 1.50 s later. How far apart are the stones when thggyfl c6fy1zr9 3sjyb1q cf6: 9 a0c3ze second one has reached a speed of 12.0 m/s ?    m

  A race car driver must average 200.0 km/h over the course of a timeh3 +ng ogvu( v0m.ra26n) gvoh trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the last lapgnhvgognrh+30.m)2a v6 ov u(?    km/h

  A bicyclist in the Tour de France creststj t qzl3526kk a mountain pass as he moves at 18 km/h . At the bottom, 4.0 km farther, his sz2kj3lq5t6k t peed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolines. The f7o1bn /jqcxjg ;e *.jmcz+ww;irst child can bounce up one-and-a-half times higher than the second child. The initial sp jxgjm w.jzb ;co7+c1e/q* nw;eed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes awl mjd-.j m08i 1.10-km-long train traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long does it take the car to pass it, and how far will the car have traveled in this time? S0 w-lj m.mijd8ee Fig. 2–40. What are the results if the car and train are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a basebald xl wa+ 1:,eje p8-)jxktx+itl with a speed of 44 m/s In throwing the baseball, the pitcher accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball durin,xa8lj)e-x:t xdi +j1t wekp +g the throwing motion.    $m/s^2$

  A rocket rises vertically, from rest, with an accelerr9 sns6yz/9 cmation of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street :)ga glvne5s-. vnr(jpattern shown in Fig. 2–42. Each intersection has a traffic signal, and the speed limit is 50 km/s . j5lnge (vsr).gna: -v Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights turn green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder traveling at a copmqf g;ad4 lndxuxld ev8( 9 sx)4w;1:nstant 120 km/h takes off in hot mq;x 4l8; )lve uxfd ndw(sax9:dg41 ppursuit. The police officer catches up to the speeder in 750 m, maintaining a constant acceleration.
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped from the roof of a building; 2.00 s afm.ld mz/ cst;4ter that, a second stone is thrown straight down with an ini.dz t; mcmls4/tial speed of 25.0 m/s and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown vertically up at the same time. The first stone in8/ az(lwsj3j s thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits the ground after 4.5 s. With what initial velocity shoul( jjz8l/3 awsnd the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long would it t-m.mr -, mg:thiq 2 d 1*hzlmbgitv-d3ake a free-falling parachutist to fall from a plane at 3200 m to an altitude of 350 m,,r:zl q3tgd*ih- 1m2m-v db-h immg .t where she will pull her ripcord? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a cohq 1g0 5z5 20wna/3y 3 srsttci5mdqponveyor belt to send the burgers through a grilling machine. If the grilling machine is 1.1 m long and the burgers require 2.5 min to cook, howt gcrw3sp5z105dha q5ytmi 03 /n2sqo fast must the conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a h-o/u1p6qvxs3)qv;f r hiad4p; 4uxsspeed 1.5 times faster than Joe can. How many times higher will Bill’d6pfsoq/h 1xa4ui3;vq-pvurs )4 ;x hs ball go than Joe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend bwy069 sg6khz s e92 9p gmk(p/wfal:bstands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with gh/p9kz gm(p 096 lbw 29ybk6fsawes :which your friend threw the ball?    m/s

  Two students are asked to find the height of a particular building using a barox)(.ddkn( (3nbdnp ls01fnk ymeter. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the other, 2.3 s. How n x )dnn f01kb kd(lp.ys((d3nmuch difference does the 0.3 s make for the estimates of the building’s height?    m

Figure 2–43 shows the position vs. time g03/ jv wq:c8(cvb ylshraph for two bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycljywqvvh 8s3b/c0 c l(:e is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?